1. Field of the Invention
The present invention relates to an adjacent track data guarantee processing method for executing guarantee processing on data of an adjacent track which is influenced by data writing on a predetermined track on a disk, and a disk device using this method, and more particularly to a guarantee processing method for adjacent track data and a disk device, which allows to execute an offset read check for the adjacent data which may have been influenced by data erasing, then to rewrite the data only when a predetermined degree or higher off track writing is detected, so that adjacent data which cannot be completely read due to off track writing is prevented.
2. Description of the Related Art
Compact and large capacity storage devices are in wide use. Such a storage device is comprised of a storage medium where many recording tracks are created concentrically or in spirals, an optical or magnetic head, and an actuator which positions the head at a desired track. The head reads or writes the data of the positioned track.
In such a disk device, the head is positioned at a desired track, and the head follows up the track by a track servo control. In this case, track pitch and other factors are designed such that even if the head writes data at a certain location of the track while being shaken within the specification limit, the written data does not influence the data of an adjacent track, and the data written while the head is shaken can be read.
Also track pitch and other factors are designed with sufficient margins so that even if the head writes data while being shaken outside the specification limit, the data of an adjacent track is not influenced. Also a device where the head is always shaken exceeding the specification limit is not shipped as a defective product.
Therefore even if data is written at a head position outside specification during data writing, only a write retry is executed until the data is written within the specification limit. In the case of a magnetic disk device, the write operation outside the specified head position stays only in one frame, since the write operation is immediately paused when it is detected that the head has written the data outside the specified position (write fault), and the sampling speed of the head for detection is sufficiently fast with respect to the shaking of the head.
As mentioned above, the magnetic disk device is designed such that adjacent data is not influenced because of mechanical reasons and the detection sampling speed, even if data is written while the head is shaken outside the specification limit in a normal working environment.
Recently, however, the density of stored data on a disk is increasing, and the track width of a disk is becoming smaller and smaller. Applications of a magnetic disk device are expanding, and now a disk device is built into not only fixed terminals but portable terminals as well. Therefore the occasions to receive shocks outside the specification limit are increasing, and the guarantee of data in such cases is demanded.
Although it is designed that adjacent track data is not influenced, the data of an adjacent track is somewhat affected (deleted) if the track is written several ten thousand times due to the characteristics of the head.
Therefore many technologies for preventing the deletion of data, by rewriting the affected data of the adjacent cylinder at the point when an off track write (write fault) beyond a certain degree is detected, have been proposed.
FIG. 18 is a diagram depicting the sector format of a magnetic disk device, where one sector is comprised of a servo section and data sections 1, 2, 3, 4, and 5, and the head is positioned by the signal of the servo section. FIG. 19 shows the format during data write, wherein the track interval is designed such that an adjacent sector positioned at the adjacent track is not influenced even if the head is shaken exceeding the specification limit during normal use.
FIG. 20 is a diagram depicting conventional processing when an off track write occurs to a magnetic disk device. When an off track write (or write fault) is detected during data write by the position of the write head, the track data of the track itself is recovered by rewriting data returning to a specified sector from the detected sector. However, the data D5 of the adjacent sector becomes difficult to read due to the off track write. If data D5 remains in this status and is influenced by an off track write from the other side of the track n+2, data D5 cannot be read at all.
Therefore when an off track write is detected, the head returns to a specified sector from the detected sector, and rewrites the data to recover the data of the track itself first, then for the data of the adjacent sector, a read operation is attempted until the data is read, and the data which is difficult to read is recovered by rewriting the data at the point when the data can be read. In FIG. 20, there is one adjacent sector to be recovered, but the data of a plurality of sectors may be recovered returning to a specified sector of the adjacent track.
For reading data as well, when the data cannot be read on the track n but can be read with offset, as shown in FIG. 21, it is judged that this data 2 has the possibility of an off track write, and this data 2 is rewritten returning to a specified sector from the detected sector to recover the data of track n first, and for the data 2 in the adjacent sector as well, a read operation is attempted and data is rewritten at the point when the data can be read so that the data which is difficult to read can be recovered.
These adjacent data guarantee processing when an off track write is detected are proposed in Japanese Patent Laid-Open No. 6-52635, Japanese Patent Laid-Open No. 11-203614, Japanese Patent Laid-Open No. 2001-14606, and Japanese Patent Laid-Open No. 2001-118343, for example.
In such prior art, adjacent data guarantee processing is executed when a write fault is detected or when a predetermined amount of offset read retries is detected. The write fault is detected when it is recognized that the position of the head exceeded the write off track slice in a frame of the target sector during data write. The value of the write off track slice is defined by the deviation of the head position from the center position of the track, and a value derived from the characteristics of the head and medium, and by research.
The write off track slice value is also determined such that the read head can read the data at the center of the track (on track) without problems, even when the head writes data with offset within this write off track slice. In the same way, guarantee processing during a read is executed when the data can be read with a predetermined head offset amount during a read retry.
Conventionally when a write fault is detected or when the data can be read by an offset read retry, it is judged unconditionally that there is the possibility that an adjacent sector may not be read, and adjacent data guarantee processing is executed by reading the adjacent sector and rewriting the data.
However, as described above, if the disk device is used for portable equipment, it is possible that a write fault will occur frequently depending on the environment of the device, such as the case of installing in a vibrating location. And the device reports the write fault to the host only when the data cannot be written normally, even if a write retry is continuously executed for a plurality of times.
Therefore if adjacent sector guarantee processing is executed each time a write fault is detected, safety is high in terms of data guarantee, but processing to read an adjacent sector and to rewrite the data occurs many times, making the performance of the device inefficient, particularly when the read/write speed drops. Also as described above, the device is designed with sufficient margins so that the occurrence of a write fault does not have the influence of disabling the reading of an adjacent sector, so it is very rare a write fault due to a strong shock influencing an adjacent sector occurs. Since write faults which do not influence an adjacent sector exist in this way, conventional adjacent sector guarantee processing executes excessive guarantee processing, which drops the high-speed reading and writing performance of the device.